The base-catalysed cyclisation of phenyl N-(2-hydroxybenzyl)-N-methylcarbamates is concerted

The kinetics of the cyclisation in aqueous solution of phenyl-(2-hydroxybenzyl)-N-methylcarbamates to 3-methyl-3,4-dihydrobenzo[e][1,3]oxazin-2-ones and phenolate ions fit the rate law: k(obs) = k(c)/(1 + [H3O+]/K-a) The values of k(c) and pK(a) fit Bronsted equations against the pK(a)'s of the corresponding free phenols but the system does not conform to the reactivity selectivity hypothesis. The values of the Bronsted parameters beta(Y) and beta(X) vary as a function of Y and X according to the equations: beta(X) = -0.179pK(a)(HY) + 0.87 beta(Y) = -0.179pK(a)(HX) + 2.30 The magnitude and sign of the Cordes-Thornton cross-interaction coefficient p(XY) (-0.179) rule out a stepwise mechanism involving a tetrahedral intermediate and is consistent with a concerted displacement mechanism. A similar concerted mechanism is proposed for the base-catalysed cyclisation of phenyl-N-(2-hydroxyphenyl)-N-methylcarbamate esters to benzoxazol-2-ones.